Types of Solar Electric Systems

Off-Grid Home

An off-grid home has its own complete, self-contained power generating station. It is independent of utility power lines (the "grid"), and all power needed by the home is produced on-site. Because they are isolated from any grid support, off-grid systems require careful matching of system capacity, energy storage capability and system loads. A typical off-grid home will have a solar PV array, a battery bank, an inverter, and a number of other components needed for system control, monitoring and safety. Off-grid home systems often include additional energy sources for use during extended periods of cloudy weather. These may include renewable sources such as a windmill or hydroelectric generator or a fossil fuel generator.

Grid-Tied Home with Battery Storage

Grid tied homes are connected to the electric utility lines. This allows the home to use and/or store solar electricity when the sun is shining and to use the electric utility's power when the sun is not out. In the event of a utility power failure, this type of system can automatically switch over to battery power. While the utility power is out, this house functions as an off-grid home. When the power comes back on, the system automatically switches back to using a combination of solar and grid-power.

The homeowner may never even know there has been a power failure. The battery system may be sized to provide enough power only for priority emergency uses, or for more typical consumption patterns. Increasing the storage and backup capacity of the system increases the cost of the system.

When batteries are fully charged and the sun is shining, the homeowner can take advantage of net metering and sell power back to the utility company at retail rates.

Grid-Tied Home without Battery Storage

Grid tied homes are connected to the electric utility lines. This allows the home to use and/or store solar electricity when the sun is shining and to access utility-provided power when the sun is not out. A grid-tied system is designed so that the electric needs of the house are first met by whatever electricity is generated by the PV system and electric utility makes up any difference.

At times when the solar panels are generating more power than is being consumed, the excess power is sent back through the electric company's power lines, spinning the utility meter backwards. As there is no method of storing energy with this type of system, when utility power fails there is no back up power and the house is without electricity. It is not possible to directly use the power from the PV array when grid-power fails.

Stand-alone

Stand-alone systems are designed for specific applications, typically in areas where grid power is not readily accessible. These applications include electric fences, human or livestock water systems, boats, traffic safety signs, telecommunications, and parking lot lighting. For most of these applications, packaged systems are available. These systems contain all of the components necessary for independent operation under a variety of environmental conditions.